WASHINGTON (Reuters) - Satellite images show that a large
hunk of Antarctica's Wilkins Ice Shelf has started to collapse
in a fast-warming region of the continent, scientists said on
Tuesday.

The area of collapse measured about 160 square miles of the
Wilkins Ice Shelf, according to satellite imagery from the
University of Colorado's National Snow and Ice Data Center.

The Wilkins Ice Shelf is a broad sheet of permanent
floating ice that spans about 5,000 square miles (13,000 square
km) and is located on the southwest Antarctic Peninsula about
1,000 miles south of South America.

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"Block after block of ice is just tumbling and crumbling
into the ocean," Ted Scambos, lead scientist at the National
Snow and Ice Data Center, said in a telephone interview.

"The shelf is not just cracking off and a piece goes
drifting away, but totally shattering. These kinds of events,
we don't see them very often. But we want to understand them
better because these are the things that lead to a complete
loss of the ice shelf," Scambos added.

Scambos said a large part of the ice shelf is now supported
by only a thin strip of ice. This last "ice buttress" could
collapse and about half the total ice shelf area could be lost
in the next few years, Scambos added.

British Antarctic Survey scientist David Vaughan said in a
statement: "This shelf is hanging by a thread."

"One corner of it that's exposed to the ocean is shattering
in a pattern that we've seen in a few places over the past 10
or 15 years. In every case, we've eventually concluded that
it's a result of climate warming," Scambos added.

Satellite images showing the collapse began on February 28,
as a large iceberg measuring 25.5 by 1.5 miles fell away from
the ice shelf's southwestern front leading to a runaway
disintegration of the shelf interior, Scambos said.

A plane also was sent over the area to get photographs of
the shelf as it was disintegrating, he added.

Scambos said this ice shelf has been in place for at least
a few hundred years, but warm air and exposure to ocean waves
are causing a breakup. In the past half century, the Antarctic
Peninsula has witnessed a warming as fast as anywhere on the
planet, according to scientists.

"The warming that's going on in the peninsula is pretty
clearly tied to greenhouse gas increases and the change that
they have in the atmospheric circulation around the Antarctic,"
Scambos said.

With Antarctica's summer melt season coming to an end, the
he said he does not expect the ice shelf to disintegrate
further immediately, but come January scientists will be
watching to see if it continues to fall apart.